1. Technical Field of the Invention
The present invention relates to a variable capacity supercharger whose flow rate of gas introduced can be adjusted.
2. Prior Art
The variable capacity supercharger in which a plurality of nozzle vanes are assembled and the rate of flow of gas to be introduced into a turbine is adjusted by controlling the throat between the nozzle vanes, have been widely used. Such supercharger is described in, for example, unexamined Japanese patent publication No. 296731/1997 and unexamined Japanese utility model publication No. 73597/1992. One of these examples is shown in FIGS. 1A and 1B. In detail, turbine housing 1 and compressor housing 2 are integrated into one body via bearing housing 3. Turbine impeller 4 in turbine housing 1 and compressor impeller 5 in compressor housing 2 are connected with turbine shaft 7 supported freely rotatably by bearing 6 in bearing housing 3. Annular turbine shroud 9 with gas discharge channel 9a is formed on the inner periphery of the above-mentioned turbine housing 1 on the side opposite to bearing housing 3 using bolts 8. Annular channel 10 is constructed between axially opposed surfaces of the outer periphery of the turbine shroud 9 and the inner periphery of turbine housing 1 on the bearing housing 3 side. On the outer surface of above-mentioned turbine housing 1 on the side opposite to bearing housing 3, cover 12 with gas outlet 11 that communicates with gas discharge channel 9a of the turbine shroud 9 is installed using bolts 13. Gas introduced from gas inlet 14 is guided to turbine impeller 4 from scroll channel 15 provided in turbine housing 1 to turbine impeller 4 through above-mentioned annular channel 10, then the gas is discharged from gas outlet 11 via gas discharge channel 9a. In this configuration, a large number of nozzle vanes 16 are arranged circumferentially in annular gas channel 10 constructed from above-mentioned scroll channel is to the outer periphery of turbine impeller 4. One end of operating shaft 17 is fixed at the each nozzle vane 16 and the other end of the shaft penetrates the outer portion of turbine shroud 9. The shaft 17 is protruded into torque transmission chamber 18 constructed between turbine shroud 9 and cover 12, and is connected to an actuator via transmission mechanism 19 in a link mechanism.
The transmission mechanism 19 is constructed as follows. Each operating shaft 17 rotatably engages with the base end of link 20, and the link is provided with engagement slot 20a at the tip end. Rotation ring 21 is arranged circumferentially on the outer part of each operating shaft 17. The same number of connecting pieces 22 as the number of the links 20 are installed freely rotatably at the rotation ring 21 via shafts 23. Each connecting piece 22 is engaged freely rotatably with engagement slot 20a of the each link 20. Pin 24 is installed at a freely selected location in the circumferential direction of the rotation ring 21. An actuator (not illustrated) is connected to pin 24 through arm 25, shaft 26, and transmission lever 27. The actuator rotates rotation ring 21, and as the rotation ring 21 revolves, an opening or closing angle of each nozzle vane 16 can be changed by means of each link 20 and operating shaft 17. Thus, the opening or closing angle of each nozzle vane 16 is controlled, and a throat between each nozzle vane 16 is adjusted to widen or narrow, so that the flow rate of gas can be varied from large to small rates.
However, in the case of a variable capacity supercharger in the above-mentioned type, because turbine shroud 9 is fixed to turbine housing 1 using bolts 8, the effect of thermal deformation in turbine housing 1 directly affects turbine shroud 9, resulting sometimes in changes in concentricity and inclination of the shroud. In addition because cover 12 is installed on turbine housing 1 with bolts 13, when transmission mechanism 19 is assembled, mounting work must be done in a blind condition, so the work is difficult. Consequently, if cover 12 is removed, the interior is inspected, and the equipment is reassembled, the results of the first adjustment often deviate from intended values because of divided transmission mechanism 19, often causing the practical problem of positional offset.